This application relates to an engine speed synchronization system for assisting an operator in manually shifting a multi-speed transmission.
Heavy vehicles typically include a multi-speed transmission controlled by a manual stick shift. An engine drives the transmission through a selectively actuated clutch. The operator selects one of several transmission speeds to result in various ratios between the input speed from the engine and the output speed of the transmission.
In trucks, there are typically ten or more different speeds available. In shifting a clutch between the speed ratios, an operator may sometimes sequentially pass rapidly through the various speeds. As an example, an operator speeding up the vehicle may quickly pass through many of the gears in rapid succession.
The operation typically required to smoothly shift a truck transmission is relatively complex. Initially, a driver actuates the clutch to break the torque transmission from the engine to the transmission. This allows the operator to move gears in the transmission out of engagement to a neutral position. The operator will then typically re-engage the clutch and attempt to synchronize the speed of the engine with a speed necessary at the next selected speed ratio to achieve a constant speed ratio at the transmission outlet. That is, the operator attempts to achieve an engine speed such that once the new speed ratio is engaged, the speed ratio of the transmission and engine will be relatively constant. Complicating the synchronization is the fact that transmission output speed will be changing. A good deal of operator experience is required to even approximate the synchronization speed. Moreover, speed synchronization typically cannot be achieved identically, and the operator must again disengage the clutch such that torque is not transmitted through the drive train as the new gear is being engaged.
This multi-step method of shifting a gear is relatively complex and time consuming. Further, it relies upon an experienced operator having a feel for the desired speed at the next selected gear. As vehicles become equipped with more complex controls, operators are required to perform more complicated operation steps. Moreover, a typical truck operator today is less experienced than in the past. Many operators lack sufficient experience to have the feel required for the shifting and speed synchronization as described above.
The prior art has proposed systems that attempt to predict the speed that would be necessary at the next selected gear ratio and begin to move the engine speed to that desired speed to achieve speed synchronization. These systems have typically been more "proposed" systems than practical production systems. As an example, the systems generally assume that a controller for the engine will always know what gear the transmission is in. In fact, since the transmission may be provided with a clutch allowing the operator to completely manually perform a shift, the controller may not always know what gear the transmission is in. Moreover, if an operator skips shifts, or performs several shifts at once, the controller may not be aware of the multiple change. Without precise knowledge of the currently engaged gear it is difficult to predict the necessary synchronization speed ratio.
Moreover, the prior art has not proposed a system that adequately predicts whether an upshift or a downshift will occur next. Without an accurate prediction of whether an upshift or downshift is occurring, the engine controller has a difficult time in rapidly identifying the necessary speed ratio and moving the engine to achieve that speed ratio.